在我的应用中，我有一个UserProfile，其中包含一个私钥。首次启动该应用程序时，它会检查pk是否存在，如果不存在，则显示输入pk的表格。所有这些都很好。现在，我在将输入的值存储到UserProfile中时遇到一些问题。这是我的表格：

import 'dart:convert';

import 'package:flutter/material.dart';
import 'package:voota/widgets/AppBar.dart';
import 'package:voota/widgets/Button.dart';
import 'package:voota/utils/Hex2Color.dart';
import 'package:voota/utils/UserProfile_dbHelper.dart';

class SetPrivateKey extends StatefulWidget {
  @override
  _PrivateKey createState() => _PrivateKey();
}

class _PrivateKey extends State<SetPrivateKey> {
  final String title = 'Set Private Key';
  final bgcolor = HexToColor('#ffffff');

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: BaseAppBar(title: title,appBar: AppBar()),backgroundColor: bgcolor,body: Center(
        child: PrivateKeyForm(),),);
  }
}

class PrivateKeyForm extends StatefulWidget {
  @override
  _PrivateKeyForm createState() => _PrivateKeyForm();
}

class _PrivateKeyForm extends State<PrivateKeyForm> {
  final GlobalKey<FormState> _formKey = new GlobalKey<FormState>();
  final TextEditingController _controller = new TextEditingController();

  var _userprofile = UserProfileDatabaseHelper().getUserProfile();

  @override
  Widget build(BuildContext context) {
    final int maxLength = 5;

    return Form(
      key: _formKey,child: new Container(
          padding: const EdgeInsets.all(30.0),color: Colors.white,child: new Container(
            child: new Center(
                child: new Column(children: [
              new Padding(padding: EdgeInsets.only(top: 20.0)),new Text(
                'Enter or Scan your Private Key',style:
                    new TextStyle(color: HexToColor("#F2A03D"),fontSize: 14.0),new Padding(padding: EdgeInsets.only(top: 30.0)),new TextFormField(
                maxLength: maxLength,decoration: new InputDecoration(
                  labelText: "Private Key",fillColor: Colors.white,border: new OutlineInputBorder(
                    borderRadius: new BorderRadius.circular(15.0),borderSide:
                        new BorderSide(color: Colors.orange,width: 2.0),validator: (value) {
                  if (value.isEmpty || value.length < maxLength) {
                    return "Enter a valid private key";
                  } else {
                    return null;
                  }
                },onSaved: (value) async {
                  print('onSaved');
                },style: new TextStyle(
                  fontFamily: "Poppins",new Container(
                child: new Row(
                  mainAxisAlignment: MainAxisAlignment.spaceEvenly,children: <Widget>[
                    new VootaButton(
                        text: 'Scan',textColor: Colors.white,buttonColor: Colors.green,onpressed: () {}),new RaisedButton.icon(
                        label: new Text("Save",style: new TextStyle(
                                color: HexToColor("#FFFFFF"),fontSize: 14.0)),icon:
                            new Icon(Icons.save,color: HexToColor("#FFFFFF")),color: HexToColor('#508bbb'),elevation: 5.0,onpressed: _submitForm),],])),)),);
  }

  void _submitForm() {
    final FormState formState = _formKey.currentState;

    if (!formState.validate()) {
      Scaffold.of(context).showsnackBar(snackBar(
        content: Text('Form is not valid,please check !!'),backgroundColor: Colors.redaccent,));
    } else {
      // hide keyboard
      FocusScope.of(context).requestFocus(Focusnode());
      // display a snackbar.
      Scaffold.of(context).showsnackBar(snackBar(
        content: Text('Processing and validating Private Key...'),backgroundColor: Colors.orange,));

      formState.save();
    }
  }
}

onSaved：执行得很好，正是在这里我需要您的帮助。我只是想更新pk（如果UserProfile已经存在），否则，请创建一个新的。欢迎任何帮助，建议或链接。谢谢。